Conventional wastewater treatment facilities are large complexes for handling tens of millions of gallons of wastewater annually. These facilities produce clean water, yet also produce significant volumes of solidified waste sludge. Disposal of the waste sludge requires handling and disposal such as in landfills or other sources.
In a typical wastewater treatment plant, the influent passes through a series of treatment processes to remove large objects and then reduce the solids and waste particles before separating residual solids from the water. A headworks provides screening and grit removal. Screening removes roots, rags, cans and large debris from the flow of influent. A low-flow section facilitates removal of grit and heavy particulates. Primary treatment includes pre-aeration with air to freshen the wastewater and help remove oils that form scum on an upper surface of the water. This primary treatment accordingly combines sedimentation and floatation in order to remove settleable and floatable materials. Thereafter, secondary treatment removes suspended and dissolved solids. The secondary treatment typically involves treatment of wastewater with activated sludge in which biologically active microorganisms assimilate waste materials. Subsequently, disinfection kills pathogenic organisms in the clarified wastewater. The resulting effluent is then generally discharged to surface waters.
In treatment facilities that use activated sludge for wastewater treatment, raw wastewater is mixed in a first aeration tank with return activated sludge. This activated sludge typically comprises relatively high concentrations of biologically active microorganisms. These organisms consume the waste products to reduce the volume of solids in the wastewater. The term "return activated sludge" comes from the source of such, a secondary clarifier, in which the microorganisms become highly concentrated. In the secondary clarifier, microorganisms and waste collect into large clumps of material known as floc. Activated sludge floc separates from the water by gravitational force and sinks towards a bottom portion of the secondary clarifier. A portion of the activated sludge i.e., is returned to the first aeration tank for mixture with raw highly concentrated influent wastewater. Finally, the separated clear water is removed to a disinfecting tank for disinfection and subsequent discharge with microorganisms to surface waters.
Activated sludge is typically measured in terms of biochemical oxygen demand (BOD) in terms of milligrams per liter (mg/l). This measures the strength of the wastewater and the primary food source for the microorganisms. The clarity of the wastewater is also evaluated in terms of total suspended solids (TSS). Domestic wastewater typically is about 250 mg/l BOD and 200 mg/l TSS. However, return activated sludge solids concentrations typically ranges between 2000 and 6000 mg/l TSS. Plant effluent is typically 10 mg/l for both TSS and BOD.
Periodically, the accumulated sludge is discharged to a dewatering facility such as a sludge lagoon or a drying bed. My U.S. Pat. No. 5,536,420 describes a vertical drainage drying bed for waste sludge. Drying beds in accordance with that invention significantly reduce the time required to remove excess water from the sludge. Dried sludge is removed from the drying bed with heavy equipment and may be used as a low-grade fertilizer.
While large scale water treatment facilities have met the need for major metropolitan areas to satisfactorily treat wastewater prior to discharge to streams and lakes, these large scale facilities are significantly expensive. In recent years, environmental concerns have increased the regulatory oversight and rules governing wastewater treatment and discharge. Smaller communities are now finding it imperative that wastewater be treated prior to discharge into streams and rivers. Natural percolation of wastewater is no longer satisfactory. However, the expense of construction and operation large scale wastewater treatment facilities has significantly increased the costs of such.
Accordingly, there is a need in the art for an low capacity modular wastewater treatment apparatus. It is to such that the present invention is directed.